Lambton Begins Trigonometrical Survey of India Summary

  • Last updated on November 10, 2022

The survey of India devised by William Lambton produced the Great Arc of the Meridian, a chain of measurements established from the south of India to the Himalayas. This survey of unprecedented magnitude resulted in the precise measurement of distances and heights throughout the Indian subcontinent and initiated the field of geodetic sciences in India.

Summary of Event

A landmark event in colonial history, the Great Trigonometrical Survey of India was an integral part of the subcontinent’s colonization during which information about the land and its population was exhaustively collected. When the survey began, colonial mapmaking had already been institutionalized under the auspices of the British East India British East India Company;Trigonometrical Survey of India Company. During the 1760’s and 1770’s, James Rennell had set the stage for this mapmaking with his general survey of Bengal. The Great Trigonometrical Survey was much more ambitious than the regional surveys undertaken by Rennell and others in the eighteenth century. It introduced new scientific methods in place of standard route surveys, which were based on the observation of hills, mountains, forts, and other landmarks visible from rivers and roads. India;trigonometrical survey of Lambton, William British Empire;Trigonometrical Survey of India [kw]Lambton Begins Trigonometrical Survey of India (Apr. 10, 1802) [kw]Begins Trigonometrical Survey of India, Lambton (Apr. 10, 1802) [kw]Trigonometrical Survey of India, Lambton Begins (Apr. 10, 1802) [kw]Survey of India, Lambton Begins Trigonometrical (Apr. 10, 1802) [kw]India, Lambton Begins Trigonometrical Survey of (Apr. 10, 1802) India;trigonometrical survey of Lambton, William British Empire;Trigonometrical Survey of India Great Trigonometrical Survey Triangulation Survey of India [g]British Empire;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] [g]India;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] [c]Exploration and discovery;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] [c]Geography;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] [c]Cartography;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] [c]Mathematics;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] [c]Earth science;Apr. 10, 1802: Lambton Begins Trigonometrical Survey of India[0150] Everest, Sir George Rennell, James

The prime mover behind the survey was William Lambton, a British veteran of the American Revolutionary War (1775-1783) who served as a regimental officer in India. In seeking funds for his project, Lambton argued that there was need for a Mathematics;and surveying[Surveying] mathematical and topographical survey of India “of the greatest accuracy.” To many in the British East India Company, Lambton’s survey was impractical, and some viewed it as a waste of time and money. In spite of his detractors, Lambton began his massive survey in 1802, ordering an enormous brass and cast-iron instrument called a theodolite from London. The instrument, which weighed about one-half ton and required twelve men to carry it, would be erected on makeshift towers or mountain peaks in order to measure the angles between markers. Foreshadowing a string of logistical and mechanical difficulties, the theodolite arrived in India only after the ship carrying it was captured by the French and taken to Mauritius.

The Great Arc of the Meridian





Lambton’s surveying process, known as “triangulation,” used trigonometric computations to determine the position of three mutually visible reference points. Beginning with the measurement of a baseline between two points, the distance to a third point could be determined by measuring the angles with the theodolite. The newly determined sides of the triangle could then become the baselines for subsequent triangulation, and a chain of triangles could thereby be constructed. This method was used to create what was known as the Great Arc of the Meridian, a continuous chain of triangles that extended the entire length of the subcontinent, from Cape Comorin in the south of India to Mussoorie in the north. The Great Arc provided the backbone for other series of arcs, such as Lambton’s Peninsular Longitudinal, constructed between 1803 and 1805, Sir George Everest’s Everest, Sir George Bombay Longitudinal (1822-1823), the Calcutta Longitudinal (1825-1831), and the Northeast Longitudinal (1840-1850).

On April 10, 1802, Lambton laid out the first baseline that would serve as the anchor for the Great Trigonometrical Survey. The first full measurement of the line’s seven and one-half miles required four hundred individual measurements with a one-hundred-foot chain. At each measurement, the extended chain was supported by five wooden coffers propped up with tripods. Each coffer was fitted with a thermometer, so measurements could be adjusted to take into account any expansion of the bars due to variations in temperature. It took fifty-seven days to complete the elaborate process of measuring the baseline. In September, Lambton began his triangulation, completing the short meridional arc from Madras to Cuddalore in order to determine the length of a degree of latitude. In October, 1804, after completing the series, Lambton headed westward and inland to carry the chain of triangles in the direction of Bangalore. With the onset of the monsoon season in 1805, Lambton began his major mission, the latitudinal measurement of the Great Arc of the Meridian. With the Bangalore base as their starting point, the triangles composing this arc extended north about one hundred miles to the territory of the nizam of Hyderabad and south toward the subcontinent’s tip.

In 1818, sixteen years after the beginning of the survey, the British government officially named it the Great Trigonometrical Survey (GTS). That same year, Lambton took on Sir George Everest Everest, Sir George as his chief assistant, and four years later, when Lambton died on the road while measuring triangulations between Hyderabad and Nagpur, Everest assumed control of the project. Known for his harsh temper and tenacity, Everest was forced to seek medical treatment in London briefly; however, the survey was resumed after his return. In 1832, Andrew Scott Waugh Waugh, Andrew Scott and Thomas Renny-Tailyour Renny-Tailyour, Thomas joined Everest to complete the northern section of the Great Arc of the Meridian. By 1834, when Everest retired, the survey had come within range of the Himalayan Mountains. The highest mountain in the range, known then as Peak XV, rose from forbidden territory on the Nepal Nepal-Tibet border, and it was therefore inaccessible to the surveyors; however, measurements taken from six different directions and averaged together determined that its height was precisely 29,000 feet. Hailed as the highest point on earth, the peak was named after Sir George Everest.

The work of surveyors in the Himalayan range led unexpectedly to new scientific findings. As the team ran the Great Arc of the Meridian into the Himalayas, they encountered curious data. Discrepancies in measurements determined by a plumb bob at different peaks displayed variations in gravity. This set of data confirmed discoveries in the Andes, where it had been shown that mountains are made of material less dense than that composing lowlands. The findings encouraged scientists to pursue the conditions of the earth’s gravitational equilibrium and ultimately to develop an idea fundamental to modern geophysics that would later be known as “isostasy.”


The Great Arc of the Meridian was the longest measurement of the earth ever attempted, and the methods by which it was constructed represent a landmark in the field of cartography. Before the Great Trigonometrical Survey of India, maps were based largely on information derived from coastal surveys or astronomical references. By contrast, the survey created a highly accurate series of measurements based directly on the landmass. Moreover, it formed a skeletal framework that could be exploited to produce detailed localized maps and topographic analyses of specific regions as necessary. It also lent itself to the measurement of heights in the Himalayan mountain range and established that Peak XV, later named Mount Everest, Everest, Mount was the highest point on earth.

From the eighteenth century, surveying and mapmaking had come to play an integral role in Britain’s administration of India. It laid the groundwork for the construction of roads, railways, power lines, and other infrastructure, and it aided the efficiency of British revenue collection. For William Lambton, however, the prime motivation for the Great Trigonometrical Survey was scientific. At the beginning of the nineteenth century, when he devised the survey, little was known about the earth’s shape and size. As he had hoped, by its completion the survey had contributed precise knowledge of the earth’s curvature at various latitudes, settling an issue that had remained outstanding in the scientific community for more than seventy years. Ultimately, the survey provided some of the most significant contributions to the advancement of geodesy and general science during the nineteenth century.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Adas, Michael. Machines as the Measure of Men: Science, Technology, and Ideologies of Western Dominance. Ithaca, N.Y.: Cornell University Press, 1989. Provides a broader context for the Great Trigonometrical Survey of India by exploring the impact of technology on history and its role in European expansion.
  • citation-type="booksimple"

    xlink:type="simple">Edney, Matthew H. Mapping an Empire: The Geographical Construction of British India, 1765-1843. New Delhi, India: Oxford University Press, 1999. This exhaustive source on British mapping describes how British visitors used modern survey techniques both to define the spatial image of the empire and to legitimate its colonialist activities.
  • citation-type="booksimple"

    xlink:type="simple">Everest, George. An Account of the Measurement of an Arc of the Meridian between the Parallels of 18°3′ and 24°7′: Being a Continuation of the Grand Meridional Arc of India. 2 vols. London: J. L. Cox, 1830. The surveyor’s own account of his process.
  • citation-type="booksimple"

    xlink:type="simple">Keay, John. The Great Arc: The Dramatic Tale of How India Was Mapped and Everest Was Named. New York: HarperCollins, 2000. A concise history of the surveying process, with illustrations, photographs, and a good map of the triangulations.
  • citation-type="booksimple"

    xlink:type="simple">Phillimore, R. H. Historical Records of the Survey of India, 1945-1958. 5 vols. n.p.: Dehra Dun, 1950-1968. Volume 3 describes the events leading up to the survey in the years 1815-1830, while volume 4 describes the contributions of George Everest between the years 1830 and 1843. Volume 5, dealing with the contributions of Andrew Waugh, was withdrawn from mass publication.
  • citation-type="booksimple"

    xlink:type="simple">Wilford, John Noble. The Mapmakers. Rev. ed. New York: Alfred A. Knopf, 2000. Chapter 11 describes the surveying methods of Lambton and Everest, as well as their contribution to general science. The text is particularly useful in describing the geodetic implications of the project.

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